1. Field of the Invention
The present invention relates to an inkjet recording apparatus and method, and more particularly, to technology for reducing the visibility of density non-uniformities (banding) in an inkjet recording apparatus which forms image on a recording medium using treatment liquid and ink.
2. Description of the Related Art
A method is known which improves optical density by preventing bleeding of ink through increasing the viscosity of ink or fixing ink by depositing droplets of treatment liquid which reacts with the ink, or applying the treatment liquid, prior to ink droplets of ink, and by maintaining coloring material of the ink in the vicinity of the surface of the recording medium (see, Japanese Patent Application Publication No. 2002-67296). In this system, a treatment liquid is used and dot bleeding is suppressed by the action of the treatment liquid. Consequently, the surface area of one dot is smaller than in a case where no treatment liquid is used. In particular, when ink droplets are deposited onto a medium other than special inkjet paper, there is a marked reduction in the dot surface area. This may result in highly conspicuous banding, which is dependent on deviation in the dot landing positions and ejection volumes. This problem is especially pronounced in line heads, which cannot perform shingling.
The main causes of deviation in the landing positions are thought to be those described in (1) to (3) below. (1) Deviation in nozzle ejection position, deviation in ejection volume, ejection failure (these occurrences are referred to jointly as “ejection errors” below). (2) Deviation from the reference position of the interval Pm in the main scanning direction between dots ejected from nozzles at the head return sections shown as A and B in FIG. 20, in a case where a head having a two-dimensional nozzle arrangement such as that shown in FIG. 20 (a head having an ejection surface in which the nozzles are arranged in a two-dimensional matrix) is installed obliquely in the plane of the ejection surface with respect to the relative movement direction of the recording medium (including cases where the recording medium is conveyed at a prescribed angle with respect to the sub-scanning direction (slanted or zigzag movement)). (3) Deviation at the joints between short heads (the nozzles at the joint sections shown as C and D in FIG. 21) in a composition where short head modules 250′ are joined together, as shown in FIG. 21. In FIGS. 20 and 21, reference numeral 252 indicates a pressure chamber, and a black circle inside a pressure chamber indicates a nozzle.
Japanese Patent Application Publication No. 2002-67296 discloses that treatment liquid (ink of enhanced printability) should not be deposited on regions where dots ejected from nozzles having an abnormal ejection state, or dots in the vicinity thereof, are to land. However, this means that application of treatment liquid is halted universally for all dots ejected from nozzles having an abnormal ejection state, regardless of the state of banding or the density of the image, and the like. Therefore, it cannot be regarded as providing a satisfactory solution to the aforementioned problems of systems based on the combination of two liquids. This is because dot bleeding occurs when this method is employed in low-density areas, and reduced density occurs when this method is used in high-density areas. In particular, this method is inadequate for resolving banding caused by situations (2) and (3) described above.